Conventionally, hybrid vehicles including an engine and motors have been developed, and in recent years, plug-in hybrid vehicles the battery of which can be charged using an external commercial power source have also been developed (Patent Document 1).
Some plug-in hybrid vehicles are configured to switch depending on the driving state between an EV mode in which the driving wheels are driven by only motors as power sources, a series mode in which the engine is used as an electric power supply source (electric generator) for the motors while the motors are used as power sources, and a parallel mode in which both the engine and the motors are used as power sources. This enables a significant reduction in fuel consumption.
Meanwhile, if the fuel to be used for the engine remains in the fuel tank or pipes for a long period of time, the fuel changes in quality and deteriorates due to oxidation, dissolution of water, and the like. For example, volatile components of the fuel evaporate, and the ratio of the fuel components sometimes becomes unsuitable. Such change and deterioration of the fuel may cause rusting in the fuel tank, or a problem that the engine will not exhibit sufficient performance when running.
In other words, hybrid vehicles have the advantage that the fuel consumption can be reduced compared to gasoline vehicles, but at the same time have the problem that it is likely the fuel remains in the fuel tank for a long period of time and causes the problems described above.
In particular, plug-in hybrid vehicles are capable of performing electric travelling for a long time by externally charging the battery, without consuming the fuel in the fuel tank fora long time. Hence, depending on the usage by the user, plug-in hybrid vehicles are used in the EV mode, in other words, used as an electric vehicle for everyday use, which makes the problems by the fuel deterioration more likely to occur.
In addition, while an engine is left unused for a long time, oil (oil film) attached to the cylinders and other parts falls off due to gravity and vibration during travelling, which decreases the protection performance against friction between metal parts. If the engine is started repeatedly without enough oil film (dry start), there is a risk of damage such as frictional wear or burning out of parts inside the engine. Moreover, leaving the engine unused for a long time sometimes causes sticking inside an injector (fuel injection device) and air entrainment in a fuel pipe, which prevent a smooth start of the engine.
In summary, while hybrid vehicles have the advantage of less fuel consumption than gasoline vehicles, there is a problem that if the engine is left unused for a long time, the problems described above are likely to occur.
In particular, plug-in hybrid vehicles are capable of performing electric travelling for a long time by externally charging the battery, without consuming the fuel in the fuel tank for a long time. Hence, depending on the usage by the user, plug-in hybrid vehicles are used in the EV mode, in other words, used as an electric vehicle for everyday use. As a result, plug-in hybrid vehicles are likely to fall into the case described above, which makes the problems caused by leaving the engine unused for a long time more likely to occur.